For anyone who is interested, just fitted the Musarri Alumium slip ons to the GPX. The originals were so quiet I couldnt hear myself let alone anyone else knowing I was there. Got them from Screamin Demon in WA arrived in four days. $320 incl delivery. Fitting was a breeze took about 15 minutes a side including removal of old ones.All the parts were supplied. Sounds great albeit a bit louder than I expected.